Generally, distribution of video signals has been carried out through coaxial cable networks used to link one or more video distribution sources with a plurality of subscribers. However, due to the high cost and minimal signal quality of such coaxial cable-based distribution networks, alternative approaches have been devised for distributing video signals. For example, telephone lines have been suggested as a physical structure for supporting distribution of video signals. However, systems using the public switched telephone network (PSTN) are often bandwidth limited, providing generally only still frame or video conferencing capabilities. In addition, because telephone system carriers only typically use the PSTN for connectivity between subscribers, the PSTN does not provide any capability for dynamic routing of digitized video without the use of dedicated leased, wide bandwidth circuits. Telephone line based systems also fail to provide acceptable VCR type functional control over the distribution of video programming.
On the other hand, an enhanced public switched telephone network does provide the capability of distributing video on demand to subscribers over the PSTN. In such an arrangement, a menu of video programming information is made accessible at a subscriber's premises. A subscriber may transmit ordering information via the PSTN to available independent video information providers. Video programming can then be accessed and transmitted to the subscriber directly from a video information provider or through a central office (CO) serving the subscriber. The video information provider is typically arranged to transmit coded digital video data over wideband PSTN connected to the CO. The video data may be buffered at the central office for transmission over a plain old telephone service (POTS) line to the subscriber. Subscribers may use either a standard telephone or a dedicated control device located at a television set to order the video programming.
The central office is connected to the various subscribers for transmission of video data coded in a digital subscriber line (DSL) type format, such as very-high-data-rate digital subscriber line (VDSL) type coding, asymmetrical digital subscriber line (ADSL) coding, or rate adaptive digital subscriber line (RADSL) type coding. In such an arrangement, multiple DSL interface units are deployed to combine video information together with bidirectional signalling and POTS for transmission over an ordinary telephone wiring plant.
However, because each type of coding format has differences in advantages and disadvantages associated therewith, particularly with respect to data transfer rates and maximum permissible length of cable run, individual video distribution providers have designed independent distribution network architectures around the type of coding best suited to their respective needs. As a result, inter-system compatibility has thus far been compromised, thereby diminishing the advantages otherwise gained by using DSL signal formatting. Therefore, a need exists for a video and data signal distribution system which can operate using different types of DSL coding format.